1. Technical Field
The present invention relates to an electronic control unit, and more particularly to an electronic control unit including a discharging circuit with a plurality of resistors connected in series, the discharging circuit being used for discharging electric charge stored in a smoothing capacitor.
2. Description of the Related Art
Conventionally, a discharging circuit configured by a plurality of resistors for discharging electric charge of a smoothing capacitor has been employed in various apparatuses. For example, Japanese Patent Application Laid-Open Publication No. 2008-172862 discloses a control apparatus including a discharging circuit used for a multiphase electric rotary machine.
This control apparatus is used for controlling a three-phase motor generator mounted on a hybrid vehicle. The control apparatus includes a capacitor, a discharge resistor, a voltage detecting circuit and a microprocessor. The capacitor is used for smoothing DC (direct current) voltage of the high voltage battery. The discharge resistor discharges the electric charge stored in the capacitor after the high voltage battery is blocked. The discharge resistor is configured by two series-connected resistor elements, and connected in parallel to the capacitor. The voltage detecting circuit detects the voltage of the lower voltage-potential-side resistor in the resistor elements and outputs the voltage to the microprocessor. The microprocessor compares the output voltage of the voltage detecting circuit with a threshold voltage and determines whether or not the discharge resistor is in an abnormal condition. Specifically, the microprocessor determines the resistor element of the discharge resistor is in abnormal condition when the output voltage of the voltage detecting circuit is a first threshold value or less, or a second threshold value or more.
In the hybrid vehicle, voltage of the high voltage battery largely varies depending on the state of the vehicle. In this regard, even if the resistor elements of the discharge resistor are in normal condition, the voltage of the lower voltage-potential-side resistor detected by the voltage detecting circuit varies. As described above, in the control apparatus, it is judged whether or not the resistor elements is in abnormal condition by comparing the output voltage of the voltage detecting circuit with the threshold voltage. Therefore, there is a concern that the judgment whether or not the resistor elements is in abnormal condition cannot be made properly.